Pulsed, Bidirectional Radio Frequency Source/Load

ABSTRACT

A radio frequency power system includes a master RF generator and an auxiliary RF generator, wherein each generator outputs a respective RF signal. The master RF generator also outputs a RF control signal to the auxiliary RF generator, and the RF signal output by the auxiliary RF generator varies in accordance with the RF control signal. The auxiliary RF generator receives sense signals indicative of an electrical characteristic of the respective RF signals output by the master RF generator and the auxiliary RF generator. The auxiliary RF generator determines a phase difference between the RF signals. The sensed electrical characteristics and the phase are used independently or cooperatively to control the phase and amplitude of the RF signal output by the auxiliary RF generator. The auxiliary generator includes an inductive clamp circuit that returns energy reflected energy back from a coupling network to a variable resistive load.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/974,947, filed on May 9, 2018, which claims the benefit of U.S.Provisional Application No. 62/504,197, filed on May 10, 2017. Theentire disclosures of the above applications are incorporated herein byreference.

FIELD

The present disclosure relates to controlling RF generators anddissipating reflected energy from a variable impedance load.

BACKGROUND

The background description provided here is for the purpose of generallypresenting the context of the disclosure. Work of the presently namedinventors, to the extent it is described in this background section, aswell as aspects of the description that may not otherwise qualify asprior art at the time of filing, are neither expressly nor impliedlyadmitted as prior art against the present disclosure.

Plasma etching is frequently used in semiconductor fabrication. Inplasma etching, ions are accelerated by an electric field to etchexposed surfaces on a substrate. The electric field is generated basedon RF power signals generated by a radio frequency (RF) generator of aRF power system. The RF power signals generated by the RF generator mustbe precisely controlled to effectively execute plasma etching.

A RF power system may include a RF generator or supply, a matching ormatch network, and a load (e.g., a plasma chamber). The RF generatorgenerates RF power signals, which are received at the matching network.The matching network matches an input impedance of the matching networkto a characteristic impedance of a transmission line between the RFgenerator and the matching network. This impedance matching aids inmaximizing an amount of power forwarded to the matching network(“forward power”) and minimizing an amount of power reflected back fromthe matching network to the RF generator (“reverse power”). Forwardpower may be maximized and reverse power may be minimized when the inputimpedance of the matching network matches the characteristic impedanceof the transmission line.

In the RF power generator or supply field, there are typically twoapproaches to applying the RF signal to the load. A first, moretraditional approach is to apply a continuous wave signal to the load.In a continuous wave mode, the continuous wave signal is typically asinusoidal wave that is output continuously by the power source to theload. In the continuous wave approach, the RF signal may be a sinusoidaloutput, and the amplitude and/or frequency of the sinusoidal wave can bevaried in order to vary the output power applied to the load.

A second approach to applying the RF signal to the load involves pulsingthe RF signal, rather than applying a continuous wave signal to theload. In a pulse mode of operation, a RF sinusoidal signal is modulatedby a modulation signal in order to define an envelope for the modulatedsinusoidal signal. In a conventional pulse modulation scheme, the RFsinusoidal signal typically is output at a predetermined frequency andamplitude. The frequency can be varied to improve impedance matchconditions, providing agile frequency tuning. Amplitude may be varied tochange the power of the RF signal. Power delivered to the load may alsobe controlled by varying the modulation signal, in addition to or ratherthan varying the sinusoidal, RF signal.

In a typical RF power generator configuration, output power applied tothe load is determined using sensors that measure the forward andreflected power or the voltage and current of the RF signal applied tothe load. Either set of these signals is analyzed to determine theparameters or electrical characteristics of the power applied to theload. The parameters can include, for example, voltage, current,frequency, and phase. The analysis may determine a power value which isused to adjust the output of the RF power supply in order to vary thepower applied to the load. In a RF power delivery system, where the loadis a plasma chamber, the varying impedance of the load causes acorresponding varying power applied to the load, as applied power ispartially a function of the impedance of the load. Therefore, thevarying impedance can necessitate varying the parameters of the powerapplied to the load in order to maintain optimum application of powerfrom the RF power supply to the load.

In plasma systems, power is typically delivered in one of twoconfigurations. In a first configuration, the power is capacitivelycoupled to the plasma chamber. Such systems are referred to ascapacitively coupled plasma (CCP) systems. In a second configuration,the power is inductively coupled to the plasma chamber. Such systems aretypically referred to as inductively coupled plasma (ICP) systems.Plasma delivery systems typically include a bias and a source that applyrespective bias power and source power to one or a plurality ofelectrodes. The source power typically generates a plasma within theplasma chamber, and the bias power tunes the plasma to an energyrelative to the bias RF power supply. The bias and the source may sharethe same electrode or may use separate electrodes, in accordance withvarious design considerations.

When a RF power delivery system drives a load in the form of a plasmachamber, the electric field generated by the power delivered to theplasma chamber results in ion energy within the chamber. Onecharacteristic measure of ion energy is the ion energy distributionfunction (IEDF). The ion energy distribution function (IEDF) can becontrolled with a RF waveform. One way of controlling the IEDF for asystem in which multiple RF power signals are applied to the load occursby varying multiple RF signals that are related by frequency and phase.The frequencies between the multiple RF power signals are locked, andthe relative phase between the multiple RF signals is also locked.Examples of such systems can be found with reference to U.S. Pat. Nos.7,602,127; 8,110,991; 8,395,322; and 9,336,995 assigned to the assigneeof the present invention and incorporated by reference in thisapplication.

RF plasma processing systems include components for plasma generationand control. One such component is referred to as a plasma chamber orreactor. A typical plasma chamber or reactor utilized in RF plasmaprocessing systems, such as by way of example, for thin-filmmanufacturing, utilizes a dual frequency system. One frequency (thesource) of the dual frequency system controls the generation of theplasma, and the other frequency (the bias) of the dual frequency systemcontrols ion energy. Examples of dual frequency systems include systemsthat are described in U.S. Pat. Nos. 7,602,127; 8,110,991; 8,395,322;and 9,336,995 referenced above. The dual frequency systems described inthe above-referenced patents include a closed-loop control system toadapt RF power supply operation for the purpose of controlling iondensity and its corresponding IEDF.

The demand on plasma processing accuracy continues to increase. Tightertolerances are being required of plasma-based fabrication systems,including decreasing component size, increasing density, both of whichrequire greater accuracy from the plasma-based fabrication processes.Further challenges exist in connection with three dimensional integratedcircuit and memory fabrication processes. One approach to significantlyincreasing the density of memory components is to fabricate memorycomponents in a three dimensional structure. Three dimensional etchingrequires tight tolerances to direct ions to carry out the fabricationprocess. Some three dimensional etching processes require a 40:1 orgreater aspect ratio. That is, the channel holes etched can be at leastforty times taller than wide. In order to properly etch to thesetolerances, it is necessary to direct ions at the wafer underfabrication in a substantially orthogonal direction, or directly at theworkpiece wafer under fabrication, to provide sufficient yields. Otherapplications that require similarly accurate directivity of the ions ata substantially orthogonal direction to the wafer include solar or flatpanel display fabrication and multiple electrode plasma fabricationsystems.

Further complicating the control of plasma-based fabrication process isthat the distribution of electrical power across the surface of a wafermay not be uniform. The electric field or electrical power near theedges of a workpiece or wafer may vary relative to the electrical poweror fields away from the edges of the wafer. This variation can cause theions to move in a direction less orthogonal to, or more across, thewafer, thereby making it difficult to meet the tolerances required forefficient fabrication, such as for three dimensional structures. Oneapproach to improving the directivity of the ions near the edge of thewafer places a secondary electrode, sometimes referred to as anauxiliary electrode, near the edge of the wafer to provide asupplemental electrical field near the edge of the wafer. The secondaryelectrode can be powered independently by a separate RF generator andenables the tuning of the electrical power and field near the edge ofthe wafer, thereby enabling an increased control of the angle ofincidence of the ions upon the wafer.

Present methods of providing RF power to the auxiliary electrode includepassive reactive termination of the auxiliary electrode, such as with avariable capacitor. Other methods include using a slave or secondary RFgenerator operating in phase lock loop with respect to a master orprimary RF generator. In a pulsed implementation, however, these methodsmay not provide the desired directivity of the ions in the plasma basedfabrication system.

SUMMARY

A RF system includes a first RF generator connected to a first electrodeof a load and generating a first RF signal to the first electrode and asecond RF generator connected to a second electrode of a load andgenerating a second RF signal to the second electrode. The first andsecond RF generators provide a respective RF voltage to the first andsecond electrodes. A controller controls the second RF generator. Thecontroller generates a control signal to at least one of the first RFgenerator or the second RF generator. The first RF generator and thesecond RF generator operate at substantially a same frequency inaccordance with a RF control signal communicated from the first RFgenerator to the second RF generator.

A RF power system for supplying a first RF power to an electrode in aload includes a processor and a memory. The memory stores instructionsexecutable by the processor and is configured to determine whether avoltage of the first RF power equals a predetermined power setpoint. Theinstructions also determine whether a phase difference between the firstRF power and a second RF power equals a predetermined phase delta, andcontrol at least one of a phase of the first RF power in accordance withthe phase difference between the first RF power and a second RF power.The instructions also vary a DC rail voltage in order to control a RFvoltage of the first RF power in accordance with an electricalcharacteristic of the first RF power, or vary a phase of the first RFpower and a DC rail voltage in order to control the first RF power inaccordance with both the phase difference between first RF power and thesecond RF power and the electrical characteristic of the first RF power.

A RF system includes a first RF generator connected to a first electrodeof a load and generates a first RF signal to the first electrode. Asecond RF generator connects to a second electrode of the load andgenerates a second RF signal to the second electrode. A controllercontrols the second RF generator and the controller generates a controlsignal to at least one of the first RF generator or the second RFgenerator. A DC power supply provides a DC rail voltage for driving apower amplifier of the second RF generator, wherein the controllervaries the DC rail voltage in order to control a RF voltage at thesecond electrode. The first RF generator and the second RF generatoroperate at substantially a same RF frequency, and the controller isconfigured to at least one of (1) vary a phase of second RF signal inaccordance with a phase difference between the first RF signal and thesecond RF signal, (2) and vary a DC rail voltage to control a RF voltageat the second electrode in accordance with an electrical characteristicof the second RF signal, wherein a DC power supply provides the DC railvoltage for driving a power amplifier of the second RF generator, or (3)vary a phase of the second RF signal and a DC rail voltage to controlthe RF voltage at the second electrode, wherein a DC power supplyprovides the DC rail voltage for driving the power amplifier of thesecond RF generator, in accordance with both the phase differencebetween first RF signal and the second RF signal and the electricalcharacteristic of the second RF signal.

A method of operating a RF power system, the method includes generatinga first RF signal applied to a first electrode of a load. A second RFsignal is applied to a second electrode of the load. A DC rail voltagedrives a power amplifier generating the second RF signal and vary the DCrail voltage in order to control a RF voltage at the second electrode.The method further includes at least one of (1) varying a phase of thesecond RF signal in accordance with a phase difference between the firstRF signal and the second RF signal, (2) varying a DC rail voltage tocontrol a RF voltage at the second electrode in accordance with anelectrical characteristic of the second RF signal, wherein the DC railvoltage drives a power amplifier generating the second RF signal, or (3)varying a phase of the second RF signal and the DC rail voltage in orderto control the RF voltage at the second electrode, wherein the DC railvoltage powers the power amplifier, in accordance with both the phasedifference between first RF signal and the second RF signal and theelectrical characteristic of the second RF signal.

A radio frequency power system is provided that includes a master RFgenerator and an auxiliary RF generator, wherein each generator outputsa respective RF signal. The master RF generator also outputs a RFcontrol signal to the auxiliary RF generator, and the RF signal outputby the auxiliary RF generator varies in accordance with the RF controlsignal. The master RF generator also generates a pulse synchronizationsignal input to the auxiliary RF generator to vary pulsing of the RFsignal output by the auxiliary RF generator.

In other features, the auxiliary RF generator receives sense signalsindicative of electrical characteristics of the respective RF signalsoutput by the master RF generator and the auxiliary RF generator.

In other features, the auxiliary RF generator determines a phasedifference between the RF signals output by the respective RF generatorsin accordance with the sense signals and generates a request to themaster RF generator to vary the RF control signal in accordance with thephase difference.

In other features, the auxiliary RF generator includes power amplifiersincluding voltage clamping circuits that return energy reflected from acoupling network to a variable resistive load. The variable resistiveload dissipates the reflected energy in accordance with a command signalthat varies the resistance of the variable resistive load.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description, the claims and the drawings. Thedetailed description and specific examples are intended for purposes ofillustration only and are not intended to limit the scope of thedisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a schematic and functional block diagram of a radio frequency(RF) power system according to various embodiments;

FIG. 2 is a schematic and functional block diagram of an auxiliary RFgenerator according to various embodiments;

FIG. 3 is a schematic and functional block diagram of an auxiliary RFgenerator configured for operation in an auxiliary mode according tovarious embodiments;

FIG. 4 is a block diagram of an auxiliary RF generator configured foroperation in a stand-alone mode according to various embodiments;

FIG. 5 is a plot illustrating waveforms in connection with operation ofthe RF power system of the present disclosure;

FIG. 6 is a flow chart depicting a phase control loop for the RF controlsystem; and

FIG. 7 is flow chart depicting a power control loop for the RF controlsystem;

FIGS. 8A-8E are waveforms of selected electrical characteristics of anexemplary RF power system depicting an oscillation under selectedconditions;

FIGS. 9A-9E are waveforms of selected electrical characteristics of anexemplary RF power system during transition of settings of a matchnetwork;

FIGS. 10A-10B are contour plots of selected electrical characteristicsof a RF power system for an initial state;

FIGS. 11A-11B are contour plots of selected electrical characteristicsfollowing transition of an RF power system from an initial state inFIGS. 10A-10B to a final state;

FIGS. 12A-12B are contour plots of selected electrical characteristicsof a RF power system in which multiple inputs effect control of selectedoutputs, according to various embodiments;

FIG. 13 is a contour plot depicting rail voltage contours of an outputvoltage under selected conditions;

FIG. 14 is a functional block diagram of a control system for a RF powersystem according to various embodiments;

FIGS. 15A-15B are plots of selected electrical characteristics of a RFpower system operating under nominal conditions;

FIGS. 16A-16B are plots of selected electrical characteristics of a RFpower system in which the response surfaces have been rotated understress conditions;

FIGS. 17A-17D are plots of selected electrical characteristics of a RFpower system controlling a single input for a selected output operatingunder nominal conditions;

FIGS. 18A-18D are plots of selected electrical characteristics of a RFpower system controlling a single input for a selected output operatingunder stress conditions;

FIGS. 19A-19D are plots of selected electrical characteristics of a RFpower system under nominal conditions controlled using the controlsystem of FIG. 14;

FIGS. 20A-20D are plots of selected electrical characteristics of a RFpower system under nominal conditions controlled using the controlsystem of FIG. 14;

FIG. 21 is a functional block diagram of an example control module inaccordance with an embodiment of the present disclosure; and

FIG. 22 is a flowchart depicting control of a multi-input, multi-outputRF power system.

In the drawings, reference numbers may be reused to identify similarand/or identical elements.

DETAILED DESCRIPTION

FIG. 1 depicts a schematic and functional block diagram of RF powersystem 10. RF power system 10 includes a master RF generator 12 and anauxiliary RF generator 14. Master RF generator 12 generates a master RFsignal 18 input to master matching or match network 20. Master matchnetwork 20 varies an impedance between master RF generator 12 andcoupling network 24 in order to achieve an impedance match betweenmaster RF generator 12 and coupling network 24 so that maximum power istransferred from master RF generator 12 to coupling network 24.Similarly, auxiliary RF generator 14 generates an auxiliary RF signal oroutput 26 to auxiliary matching or match network 28. Auxiliary matchnetwork 28 varies an impedance between auxiliary RF generator 14 andcoupling network 24 to provide an impedance match between auxiliary RFgenerator 14 and coupling network 24 to maximize power transfer fromauxiliary RF generator 14 to coupling network 24. In variousembodiments, a direct current (DC) bus 16 provides DC voltage to one orboth of master RF generator 12 and auxiliary RF generator 14.

Master match network 20 outputs a master matched RF signal 22 tocoupling network 24. Auxiliary match network 28 outputs an auxiliarymatched RF signal 30 to coupling network 24. In various embodiments,auxiliary match network 28 may have an external input (not shown). Invarious embodiments the external input receives an external signal thatcontrols the position of one or a plurality of capacitive components ofauxiliary match network 28 to vary the impedance of auxiliary matchnetwork 28. Master matched RF signal 22 and auxiliary matched RF signal30, in various embodiments, can communicate with the same or separateelectrodes of coupling network 24. In various embodiments, mastermatched RF signal 22 is applied to a master electrode 32 of a couplingnetwork 24, and auxiliary matched RF signal 30 is applied to anauxiliary electrode 40 of coupling network 24. In various embodiments,main electrode 32 and auxiliary electrode 40 are capacitively coupled,as indicated by capacitor 44, shown in phantom to indicate thecapacitive aspect of the coupling. In various embodiments, couplingnetwork 24 can be a plasma chamber, plasma reactor, or other load.

Throughout the specification, RF power system 10 can be considered ashaving components associated with a master portion of the RF powersystem 10 and components associated with an auxiliary portion of the RFpower system 10. Components associated with the master portion may bereferred to as master, main, first, or primary components. Componentsassociated with the auxiliary portion of RF power system 10 may bereferred to as auxiliary, slave, secondary, or second components.

Master matched RF signal 22 and auxiliary matched RF signal 30 cooperateto generate a reaction within coupling network 24. In variousembodiments, master RF generator 12 generates a 100 kHz-2 MHz RF outputsignal and may commonly be referred to as a bias RF generator. The biasRF generator typically accelerates positive ions from the plasma to thesubstrate surface to control ion energy and etch anisotropy. In variousembodiments, auxiliary RF generator 14 operates at the same frequency asmaster RF generator 12. A generator (not shown) may supply RF power tocoupling network 24 via a 13 MHz-100 MHz signal and may be referred toas a source RF generator. The source RF generator provides energy toignite a plasma in coupling network 24.

According to various embodiments, master RF generator 12 and auxiliaryRF generator 14 include multiple ports to communicate externally. MasterRF generator 12 includes a pulse synchronization output port 34, adigital communication port 36, and an RF output port 38. Auxiliary RFgenerator 14 includes an RF input port 42, a digital communication port46, and a pulse synchronization input port 48. Pulse synchronizationoutput port 34 outputs a pulse synchronization signal 50 to pulsesynchronization input port 48 of auxiliary RF generator 14. Digitalcommunication port 36 of master RF generator 12 and digitalcommunication port 46 of auxiliary RF generator 14 communicate via adigital communication link 52. RF output port 38 generates a RF controlsignal 54 input to RF input port 42. In various embodiments, RF controlsignal 54 is substantially the same as the RF control signal controllingmaster RF generator 12. In various other embodiments, RF control signal54 is the same as the RF control signal controlling master RF generator12, but is phase shifted within master RF generator 12 in accordancewith a requested phase shift generated by auxiliary RF generator 14.Thus, in various embodiments, master RF generator 12 and auxiliary RFgenerator 14 are driven by substantially identical RF control signals orby substantially identical RF control signal phase shifted by apredetermined amount.

Auxiliary RF generator 14 also includes a pair of sensor ports, mainsense port 60 and auxiliary sense port 62, which receive a voltagesignal from respective master voltage sensor 64 of master match network20 and auxiliary voltage sensor 66 of auxiliary match network 28. Invarious embodiments, master voltage sensor 64 senses the voltage ofmaster matched RF signal 22 to determine the voltage of master matchedRF signal 22 applied to coupling network 24. Similarly, auxiliaryvoltage sensor 66 senses the voltage of auxiliary matched RF signal 30applied to coupling network 24.

According to various embodiments, master voltage sensor 64 and auxiliaryvoltage sensor 66 detect operating parameters of the respective matchedRF signals 22, 30. While described herein as voltage sensors, oneskilled in the art will recognize that master voltage sensor 64 andauxiliary voltage sensor 66 may comprise voltage, current, and/ordirectional coupler sensors to detect selected electricalcharacteristics. In various embodiments, master voltage sensor 64 andauxiliary voltage sensor 66 may detect (i) voltage v and current iand/or (ii) forward (or source) power P_(FWD) output from respectivematched RF signals 22, 30 and/or reverse (or reflected) power P_(REV) ofmaster matched RF signal 22 and auxiliary matched RF signal 30. Thevoltage v, current i, forward power PFWD, and reverse power PREV may bescaled and/or filtered versions of the actual voltage, current, forwardpower, and reverse power associated with the respective matched RFsignals 22, 30. In various embodiments, master voltage sensor 64 andauxiliary voltage sensor 66 may be analog and/or digital sensors. In adigital implementation, master voltage sensor 64 and auxiliary voltagesensor 66 may include analog-to-digital (A/D) converters and signalsampling components with corresponding sampling rates.

In various embodiments, voltage sensors 64, 66 are configured todetermine an electrical characteristic of respective master RF signals18, 26. In various other embodiments, voltage sensors 64, 66 areconfigured to detect an electrical characteristic of respective matchedRF signals 22, 30. When voltage sensors 64, 66 are configured to detectthe voltage of respective matched RF signals 22, 30, respective matchedRF signals 22, 30 will reflect a phase shift typically introduced byrespective match networks 20, 28. If voltage sensors 64, 66 areconfigured to detect an electrical characteristic of respective RFsignals 18, 26, the sensor signals input to respective sense ports 60,62 will not reflect the phase shift introduced by respective matchnetworks 20, 28 to the respective matched RF signals 22, 30. In variousembodiments, therefore, it may be necessary for the signals input torespective sense ports 60, 62 to be post processed to approximate thephase shift introduced by respective matched networks 22, 28.

One skilled in the art will recognize that master match network 20 andauxiliary match network 28 can be implemented as separate components orcombined into a single component. Further, one skilled in the art willrecognize that master voltage sensor 64 and auxiliary voltage sensor 66can be implemented integrally with respective match networks 20, 28 orimplemented separately from respective match networks 20, 28 and placedeither upstream or downstream of respective match networks 20, 28.

In operation, master RF generator 12 generates master RF signal 18, andmaster match network 20 introduces a matching impedance into master RFsignal 18 to generate master matched RF signal 22. Similarly, auxiliaryRF generator 14 generates auxiliary RF signal 26, and auxiliary matchnetwork 28 introduces a matching impedance into auxiliary RF signal 26to generate auxiliary matched RF signal 30. Operation of auxiliary RFgenerator 14 is coordinated with respect to master RF generator 12,thereby defining a master/slave relationship. Master RF generator 12outputs an RF control signal 54 from RF output port 38. RF controlsignal 54 is input to RF input port 42 of auxiliary RF generator 14. RFcontrol signal 54 can be a digital or analog signal and defines the RFoperating frequency for auxiliary RF generator 14. When master RFgenerator 12 and auxiliary RF generator 14 are operating in a pulse modeof operation, as described above, master RF generator 12 generates pulsesynchronization signal 50 from pulse synchronization output port 34.Pulse synchronization signal 50 is input to pulse synchronization inputport 48 of auxiliary RF generator 14. Thus, the RF frequency and thepulsing of auxiliary RF generator 14 is controlled by inputs from masterRF generator 12.

In various embodiments, auxiliary RF generator 14 communicates withmaster RF generator 12 via digital communication link 52 via respectivedigital communication ports 36, 46. Digital communication link 52enables auxiliary RF generator 14 to communicate with master RFgenerator 12 to request adjustments to the RF control signal 54 toenable auxiliary RF generator 14 to align matched RF signals 22, 30 asmeasured by respective voltage sensors 64, 66.

In various embodiments, main sense port 60 and auxiliary sense port 62communicate with respective voltage sensors 64, 66 to receiveinformation about the respective matched RF signals 22, 30. Respectivevoltage sensors 64, 66 enable auxiliary RF generator 14 to determine theamplitude of respective matched RF signals 22, 30 and phase of therespective matched RF signals 22, 30. In various embodiments, theamplitude and phase of the RF signal may be controlled for each pulsestate of the respective RF generators 12, 14. Amplitude and phase datais processed by auxiliary RF generator 14 in order to determine propersynchronization between master matched RF signal 22 and auxiliarymatched RF signal 30. Once auxiliary RF generator 14 determinescorrective adjustments to achieve proper synchronization, auxiliary RFgenerator 14 communicates with master RF generator via digitalcommunication link 52 in order to communicate a desired phaseadjustment.

Master RF generator 12 receives adjustment requests from auxiliary RFgenerator 14 and adjusts the phase of RF control signal 54 in accordancewith the adjustment request. The phase of auxiliary matched RF signal 30is, thus, phase locked to the phase of the master matched RF signal 22.In various embodiments, auxiliary RF generator 14 communicates otherdata to master RF generator. The other data may include pulsinginformation.

In various embodiments, master RF generator 12 determines the RFoperating frequency of auxiliary RF generator 14. Master RF generator 12can implement an agile frequency tuning (AFT) approach to minimizingreflected power. Master RF generator 12 can also set pulse conditions inaccordance with desired pulse repetition rate, power levels, and dutycycles. In various embodiments, auxiliary RF generator 14 generates RFpower at the frequency determined by master RF generator 12 and is phaselocked to operation of master RF generator 12.

FIG. 2 depicts a schematic and functional block diagram of an expandedview of auxiliary RF generator 14. Auxiliary RF generator 14 includes acontroller section 100, a signal generation section 102, a poweramplifier section 104, an energy dissipation section 106, and a DCgeneration section 108. Controller section 100 includes a control moduleor controller 110 which further includes an auxiliary RF detectorsmodule 112, a main RF detectors module 114, an RF actuator module 116,and a customer interface 118. Auxiliary RF generator 14 may furtherinclude memory 122. Memory 122 may be used to store set, predetermined,and/or detected voltages, phases, and other operating parameters.

Auxiliary RF detectors module 112 communicates with main sense port 60and auxiliary sense port 62. Auxiliary RF detectors module 112 receivesmain and auxiliary voltage sensor signals from respective master voltagesensor 64 and auxiliary voltage sensor 66 via respective main sense port60 and auxiliary sense port 62. Auxiliary RF detectors module 112 ofcontroller 110 determines the amplitude and phase (the relative phase orphase difference) of the respective master RF output and auxiliary RFoutput (either pre- or post-match network) and determines whether aphase or amplitude correction is necessary. The phase correction iscommunicated to master RF generator 12 via digital communication link52. Auxiliary RF detectors module 112 communicates a desired phasecorrection via status/control line and communication module 126.

Controller 110 also includes main RF detectors module 114 whichdetermines selected electrical characteristics of the RF output frompower amplifier section 104. Main RF detectors module 114 communicateswith controller 110 regarding the state of RF signal or output 26.Controller 110 also includes RF actuator module 116. RF actuator module116 receives the pulse synchronization signal 50 via pulsesynchronization input port 48. RF actuator module 116 also receives anRF detection signal from RF synchronization module 142, as will bedescribed in greater detail herein. RF actuator module 116 generatescontrol signals to control, in various modes, both the frequency andpower of the continuous wave RF signal component of RF output 26 and thepulsing component of RF output 26.

Signal generation section 102 includes RF switch module 140 whichreceives RF control signal 54 from master RF generator 12 via RF inputport 42. RF control signal 54 is communicated to RF switch module 140.RF switch module 140 also receives a pulse input from RF actuator module116. The pulse input is generated by RF actuator module in accordancewith pulse synchronization signal 50 received at pulse synchronizationinput port 48. RF switch module 140 controls generation of a pulsedsinusoidal signal, as will be described herein.

As will be described in greater detail herein, RF synchronization module142 enables operation of auxiliary RF generator 14 as slave RF generatoror as a stand-alone generator in which the RF sinusoidal component ofthe RF output signal is generated independently of master RF generator12. In the slave configuration of auxiliary RF generator 14, in whichmaster RF generator 12 controls operation of auxiliary RF generator 14,RF synchronization module 142 effectively passes through the pulsed RFsignal received from RF switch module 140 and generates a pair of RFsignals input to phase shifter module 144. Phase shifter module 144receives pulse amplitude control signal from RF actuator module 116.Pulse amplitude control signal determines the relative phase shiftbetween the pair of pulsed RF signals input to phase shifter module 144.Phase shifter module 144 generates a pair of phase shifted signals phi1146 and phi2 148 which are output from signal generation section 102.

Phase shifted signals phi1 and phi2 are output to power amplifiersection 104. The pair of phase shifted signals are input to driver 152.Driver 152 generates respective drive signals to power amplifiers 154,156. The outputs from power amplifiers 154, 156 are combined and inputto filter 158. In various embodiments, filter 158 may be a harmonicfilter to remove harmonics and generate a filtered signal input to VIsensor 160. VI sensor 160 may be one of a voltage/current sensor ordirectional coupler as described above. Auxiliary RF generator 14 thusprovides a pulsed, RF output 26.

Phil provides a drive signal for power amplifier 154, and phi2 providesa drive signal for power amplifier 156. In various embodiments, poweramplifiers 154, 156 are driven by the drive signals to enable outphasingof power amplifiers 154, 156. Outphasing controls the amplitude of theoutput signal of power amplifier section 104 by varying the phasebetween power amplifiers 154, 156 by varying phi1 and phi2. One skilledin the art will recognize that various applications need not implementoutphase signal generation and that various embodiments may use a singledrive signal and power amplifier.

VI sensor 160 may be implemented as described above in connection withdirectional couplers and VI sensors. VI sensor 160 outputs a pair ofsensor signals to analog front-end 164 of signal generation section 102.Analog front-end 164 receives analog signals from VI sensor 160 andgenerates digital signals input to main RF detectors module 114. VIsensor 160, analog front-end 164, and main RF detectors 114 enablemeasuring various electrical characteristics of the RF output fromauxiliary RF generator 14.

In various embodiments, power amplifiers 154, 156 are configured toinclude voltage clamping circuits, such as inductive voltage clampingcircuits. Examples of such system can be found with reference to U.S.Pat. Nos. 6,469,919; 6,618,276; 6,885,567; 7,180,758; and 7,397,676assigned to the Assignee of the present application and incorporated byreference in this application.

Power amplifiers 154, 156 receive DC power generated from DC generationsection 108. DC generation section 108 includes an AC/DC converterreceiving a three phase AC input signal and generating a DC outputsignal. AC/DC converter 170 generates an agile DC supply voltage onvoltage rails supplying respective power amplifiers 154, 156. AC/DCconverter 170 generates a variable DC output voltage to thereby vary theamplitude of the RF signals output by respective power amplifiers 154,156. Controller 110 of control section 100 communicates with AC/DCconverter 170 via power supply unit (PSU) interface so that controller110 can both monitor and vary operation of AC/DC converter 170 in orderto generate desired rail voltages to power amplifiers 154, 156. DC bus16 is shown connected to AC/DC converter 170. In FIGS. 2-4, DC bus 16 isshown in dotted lines to indicate that it can connect in variousconfigurations to the respective main RF generator 12 and auxiliary RFgenerator 14.

DC generation section 108 communicates with energy dissipation section106. Energy dissipation section 106 includes a variable resistive load172 connected to the voltage rails connecting AC/DC converter 170 andpower amplifiers 154, 156. Variable resistive load 172 provides acurrent drain or sink for power reflected from the load connected to RFoutput 26. In various embodiments, coupling network 24 reflects ortransmits power back towards power amplifiers 154, 156. The voltageclamp circuits of power amplifiers 154, 156 return thereflected/transmitted power to variable resistive load 172 where theenergy/power is dissipated. In various embodiments, reflectedenergy/power is dissipated in AC/DC converter 170, without theassistance of variable resistive load 172. However, in various otherembodiments, AC/DC converter 170 is sized so that the power reflectedfrom coupling network 24 is greater than the power dissipationcapabilities of AC/DC converter 170. Variable resistive load 172 can becontrolled via load control signal from controller 110 in order to varythe energy or reflected power dissipated via the inductive clampingcircuits of power amplifiers 154, 156. Load control signal generated bycontroller 110 can use a pulse width modulation or a pulse densitymodulation signal to vary the impedance of variable resistive load 172,thereby variably controlling the power sourced from coupling network 24towards power amplifiers 154, 156.

Referring to coupling network 24, as discussed above, in variousembodiments, it is desirable to control the ion angle so that the ionsare directed orthogonally at the workpiece or wafer in order to bettercontrol the etching process. As also described above, electrical powerand fields near the edges of the wafers often present additionalchallenges accurately controlling ion directivity towards the wafer. Byvarying the resistance of the variable resistive load 172, ions near theedge of the wafer can be better directed to effect a more accurateetching process.

RF synchronization module 142 operates variably depending upon whetherauxiliary RF generator 14 is operated in an auxiliary ormaster/stand-alone mode. Stand-alone mode occurs when auxiliary RFgenerator 14 operates independently of master RF generator 12. RFsynchronization module 142 receives a mode signal from RF actuatormodule 116 of controller 110 that indicates whether auxiliary RFgenerator 14 is operating in an auxiliary mode or a master/stand-alonemode.

In an auxiliary or slave mode, signals phi1, phi2 output by RF actuatormodule 116 to RF synchronization module 142 have no effect. The RFsignal received from RF switch module 140 is passed through RFsynchronization module 142. Phase shifter module 144 generates drivecontrol signals phi1 and phi2 in accordance with the pulse amplitudecontrol signal received from RF actuator module 116.

In a master/stand-alone mode, auxiliary RF generator 14 relies upon RFactuator module 116 for controlling to a desired RF signal frequency. Invarious embodiments in a master/stand-alone mode, auxiliary RF generator14 receives pulse synchronization signal 50 from pulse synchronizationinput port 48. In other various embodiments in a master/stand-alonemode, RF actuator module 116 determines a synchronization pulse. Also ina master/stand-alone mode, RF synchronization module 142 and phaseshifter module 144 operate in a pass-through mode, as RF actuator module116 generates drive signals phi1 and phi2 passed through to driver 152.In the stand-alone mode, power amplifiers 154, 156 are operated in anoutphase manner, to vary the phase between power amplifiers 154, 156, inorder to control the output power of auxiliary RF generator 14. In theauxiliary mode, variable resistive load 172 provides a dissipative loadto variably dissipate power reflected from coupling network 24.

FIG. 3 depicts a structural and functional block diagram of theauxiliary RF generator 14′ of the RF power system 10 configured tooperate in an auxiliary or slave mode. Components from auxiliary RFgenerator 14 of FIG. 2 for enabling operation in a stand-alone mode havebeen removed to provide a simplified configuration of an RF generator inan auxiliary slave mode. In the configuration of FIG. 3, auxiliary RFgenerator 14′ operates as described above with respect to FIGS. 1 and 2.Auxiliary RF generator 14′ of FIG. 3 will not operate in a master orstand-alone mode.

FIG. 4 depicts a functional and structural block diagram of auxiliary RFgenerator 14″ of RF power system 10 configured to operate in master orstand-alone mode. Components of auxiliary RF generator 14 of FIG. 2 forenabling operation in auxiliary mode have been removed. In this mode,auxiliary RF generator 14″ does not require external RF signal input todetermine the frequency of the RF signal it generates. In FIG. 4, pulsesynchronization input port 48 receives pulse synchronization signal 50,which is input to RF actuator module 116 of controller 110. Pulsesynchronization signal 50 controls the pulsing of the RF output ofauxiliary RF generator 14″. RF actuator module 116 does not generatepulse amplitude control signal to phase shifter module 144. Rather, RFactuator module 116 generates phi1 and phi2 signals input to driver 152.The auxiliary RF generator 14″ of FIG. 4 does not include a variableresistive load 172, such as is shown in FIGS. 2 and 3. In variousembodiments, the power amplifiers 154, 156 include inductive clamps, andpower reflected from coupling network 24 to auxiliary RF generator 14can be returned to AC/DC converter 170. In various other embodiments asshown in FIG. 4, AC/DC converter 170 will typically output a higherpower and, therefore, variable resistive load 172 may be optional todissipate likely power levels returned from coupling network 24. Invarious other embodiments, the inductive clamps of power amplifiers 154,156 can return energy to the master RF generator 12 via a DC busconnection, such as DC bus 16 and such energy flow may be communicatedthrough AC/DC converter or bypass AC/DC converter 170. If the energyflow bypasses AC/DC converter 170, DC bus 16 may be configured as shownin FIG. 4.

In the various embodiments described herein, the master and the slavecan operate at the same frequency because drive signals originate at acommon point in the system. Transient voltage spikes may occur in aphase lock loop (PLL) implementation during rapid frequency or amplitudechanges. The direct path of the phase shifted master RF control signal54 to the auxiliary power amplifiers 154, 156 of the present disclosurewill prevent transient voltage spikes. Further, the integrated inductiveclamp and variable resistive loads increase the range of voltage controlat the electrode and the coupling network to which the auxiliary RFgenerator 14 provides power.

In various embodiments, auxiliary RF generator 14 can function as amaster RF generator and master RF generator 12 can function as anauxiliary RF generator. That is, auxiliary RF generator 12 and thecontroller 110, in various embodiments, control the rail voltage topower amplifiers 154, 156 and the phase of RF output signal 26. Invarious other embodiments, controller 110 of auxiliary RF generator 14also generates control signals input to master RF generator 12 tocontrol the voltage and phase of master RF signal 18, includingcontrolling a DC rail voltage in master RF generator to vary the voltageof master RF output signal 18 and controlling the phase of master RFsignal 18 to control a phase difference between the RF signals output byrespective auxiliary RF generator 14 and master RF generator 12. Invarious embodiments, auxiliary RF generator 14 outputs a RF signal tomaster RF generator 12 via RF input port 42, in which case RF input port42 operates as an output port or an input/output port. Phase shiftingbetween the RF output signals 18, 26 (or 22, 30) can occur when shiftermodule 144 effects a phase shift of RF output signal 26 relative the RFsignal sent to master RF generator 12 via (reversed) input port 42.Alternatively, master RF generator 12 can include a phase shifter modulesimilar to phase shifter module 144, and auxiliary RF generator 14 canoutput a commanded phase shift to master RF generator 12 via digitalcommunication port 46 for application by a phase shifter local to mainRF generator 12. Further, in various embodiments, main sense port 60 andauxiliary sense port 62 can be configured when master RF generator 12.In such a configuration, master RF generator 12 and auxiliary RFgenerator 14 can communicate sensed electrical characteristicinformation using digital communication ports 36, 46.

FIG. 5 depicts exemplary plots of RF signals of the RF power system 10according to various embodiments. Waveform 200 depicts a RF signaloutput by master RF generator 12, such as master matched RF signal 22.Waveform 202 depicts a RF signal output by auxiliary RF generator 14,such as auxiliary RF signal 26. Waveforms 200 and 202 indicate achallenge that the present embodiments address. As can be seen whencomparing waveforms 200 and 202, a phase difference exists betweenwaveforms 200 and 202. Because match networks 20, 28 introduce differentphase shifts, waveforms 200 and 202 are not phase-aligned. Waveforms 204and 206 depict one improvement provided by the embodiments of thepresent disclosure.

Waveform 204 represents a matched RF signal 20 output from master matchnetwork 20. Waveform 204 has a thickness to indicate frequency contentintroduced into waveform 204 from other generators in RF power system10, such as from a source RF generator. Waveform 206 depicts an examplewaveform of auxiliary matched RF signal 30 output from auxiliary matchnetwork 28. Waveform 206 is also depicted with a thickness to indicatehigh frequency content, such as from a source RF generator, althoughwaveform 206 includes less frequency content than waveform 204. As canbe seen, waveforms 204 and 206 depict phase aligned RF signals, as wouldbe output by master RF generator 12 and auxiliary RF generator 14.

FIG. 6 depicts a flow chart 300 for adjusting the phase of the auxiliaryRF generator, relative to the main RF generator. Control begins at block302 and proceeds to block 304. Block 304 measures the phase differencebetween the main and auxiliary RF generators. Once the phase differencehas been measured, control proceeds to block 306, where it is determinedif the phase difference is zero. If the phase difference is zero, noadjustment is required, and control returns to block 304 to againmeasure the phase difference between the main RF generator and theauxiliary RF generator. If the phase difference is not zero, controlproceeds to block 308 in which the auxiliary RF generator sends commandsto the master RF generator to request that the master RF generatorchange the phase of the RF generator. Control proceeds to block 304 toagain measure the phase difference between the main RF generator and theauxiliary RF generator.

FIG. 7 depicts a flow chart 320 for determining the voltage or poweroutput of the auxiliary RF generator. Control begins at block 322 andproceeds to block 324. Block 324 measures the voltage of the RF outputof the auxiliary RF generator. Once the voltage has been measured,control proceeds to block 326, where it is determined if the measuredvoltage is equal to a predetermined setpoint. If the measured voltage isequal to the predetermined setpoint, control proceeds to block 324 toagain measure the voltage of the auxiliary generator RF output. If themeasured voltage is not equal to the predetermined setpoint, controlproceeds to block 328. At block 328, the output of the agile DC powersupply is adjusted in order to vary the rail voltage applied to thepower amplifiers of the auxiliary RF generator. Control proceeds toblock 324 to again measure the voltage of the RF output of the auxiliaryRF generator.

In various configurations, the RF control system of FIG. 1 is tunablewithin a predetermined operating space. For example, auxiliary matchnetwork 28 of FIG. 1 is typically controlled by selecting the positionof a variable capacitance in auxiliary match network 28. In variousconfigurations, a full range of positions of the variable capacitance isnot always available, particularly over the entire operating space. Theoperating space in which a variable capacitance can be positioned toenable system operation is typically referred to as a tunable operatingspace. Preferably, the tunable operating space can be maximized. Forexample, auxiliary match network 28 may include a variable capacitancecapable of adjustment to multiple positions. However, in variousembodiments, only selected positions are available within predeterminedfrequency ranges. By way of non-limiting example, if the auxiliary RFgenerator 14 operates at up to 400 kHz, changing between positions atgreater than a predetermined frequency, such as 380 kHz, results inextended settling times and oscillation between voltage and phasecontrol loops for the RF signal applied auxiliary electrode 40. Whenoutside of the tunable operating space, the control challenges includeinstability near an edge of the actuator range and oscillation orhunting for steady state values of auxiliary voltage and phase at higherfrequencies.

FIGS. 8A-8E indicate the relationship between various electricalparameters for the RF power control system 10 of FIG. 1. FIG. 8A depictsvoltage waveforms for the main voltage 400 and the auxiliary voltage 402at the output of respective main match network 20 and auxiliary matchnetwork 28, respectively. The main voltage 400 and auxiliary voltage 402may be measured in other places in the circuit of FIG. 1, according tovarious embodiments, including the respective main electrode 32 andauxiliary electrode 40. FIG. 8B depicts a waveform 404 indicating thenet power in watts delivered by auxiliary RF generator 14. FIG. 8Cdepicts a waveform 406 indicating the phase difference in degreesbetween the RF signals applied to respective main electrode 32 andauxiliary electrode 40. FIG. 8D depicts a waveform 408 indicating therail voltage V_(RAIL) of the agile DC power supply voltage of FIG. 2 asset by a voltage actuator. FIG. 8E depicts a waveform 410 indicating therelative phase setpoint commanded by a phase actuator of auxiliary RFgenerator 14. The described phase, phase setpoint, or phase actuator isthus the desired phase determined by controller 110 of FIG. 2. In thecase of a pulse RF envelope, the waveforms in FIG. 8 indicate themeasured values for a given pulse state. For example, in the case of apulse waveform with 4 states, there will be four measured values, onefor each pulse state. Each pulse state results in a set of waveforms asin FIGS. 8A-8E indicating the respective values for each pulse state. Inthe case of continuous wave (CW) operation, there will be only one setof waveforms, similar to FIGS. 8A-8E. The controller 110 addresses eachpulse state separately and smoothly transitions between state as theyprogress from 1 . . . n and then repeat.

As can be seen in FIGS. 8A-8E, starting at time T₁, an adjustment to thephase and rail voltage actuators of auxiliary RF generator 14, withoutconsideration of the cross-term effects between the control loops,results in oscillation of waveforms 400, 402, 404, 406, 408, and 410.That is, the phase and rail voltage are adjusted independently. Thephase is adjusted according to one control loop, and the rail voltage isadjusted according to a second control loop. The independent controlleads to oscillation of the waveforms in FIGS. 8A-8E, the oscillationresults in a corresponding instability, which inhibits the settling ofwaveforms 400-410.

FIGS. 9A-9E depict electrical characteristics similar to FIGS. 8A-8Eand, therefore, the waveforms of 9A-9E will be referred to using likereference numerals from FIGS. 8A-8E. FIG. 9E indicates the responseresulting from a transition in the variable capacitance of auxiliarymatch network 28. At time T₁, which represents a change in the processresulting in adjustment of one or both of the rail voltage V_(RAIL) andthe phase of auxiliary RF generator, the rail voltage 412 and the phase410 initially diverge, as shown at respective points 412, 414, away fromthe settled or steady state values around time T₂ and beyond. In otherwords, upon the transition, the commanded rail voltage waveform 408 ofFIG. 9D should increase from the rail voltage prior to time T₁ in orderto reach a stable condition at T₂. However, as shown at point 412, railvoltage V_(RAIL) decreases, rather than increases, before eventuallyconverging to the value at time T₂. Likewise, the commanded phase atpoint 414 increases, rather than decreases, before converging to thesettled value at time T₃. In other words, in response to the transition,both rail voltage and phase waveforms 408, 410, respectively, initiallyadjust away from their eventual settled value.

FIGS. 10A and 10B depict example contour plots of a RF system having amain and an auxiliary electrode. The contour plot of FIG. 10A will bedescribed in detail. The description of the contour plot of FIG. 10Agenerally applies to the contour plots described throughout thespecification. In FIG. 10A, the x-axis represents a phase or phasesetpoint as defined by a phase actuator. The y-axis represents a railvoltage V_(RAIL). The phase of the x-axis and the rail voltage V_(RAIL)of the y-axis define two inputs for varying a delta phase defined along,in three dimensional space, a z-axis. In order to represent the z-axisin two dimensional space, contour lines 420 a, 420 b . . . , 420 gdefine lines of constant delta phase. The delta phase is generallydefined as the phase difference between the RF signal applied to mainelectrode 32 and the RF signal applied to auxiliary electrode 40. Invarious embodiments, contour line 420 a corresponds to −D₂, indicating anegative delta phase or phase lag of the RF signal applied to auxiliaryelectrode 40 relative to the RF signal applied to main electrode 32.Contour line 420 b corresponds to delta phase −D₁, contour line 420 ccorresponds to a 0 delta phase, contour line 420 d corresponds to deltaphase D₁, contour line 420 e corresponds to delta phase D₂, contour line420 n corresponds to delta phase D₃, and contour line 420 g correspondsto delta phase D₄. The regions between the contour lines represent atransition in delta phase, which may be gradual or severe, between therespective contour lines.

FIG. 10A indicates the delta phase that corresponds to a particularcombination of phase of the RF signal applied to auxiliary electrode 40and the rail voltage V_(RAIL) for auxiliary RF generator 14. Asdescribed above, rail voltage V_(RAIL) represents the output of agile DCpower supply and applied to respective power amplifiers 154, 156. By wayof non-limiting example, point 422 of FIG. 10A indicates that for agiven phase (x-axis) and rail voltage V_(RAIL) (y-axis), the deltaphase=0. That is, for phase x=a and rail voltage V_(RAIL) y=b, the deltaphase Level=0 (z=0).

FIG. 10B is a contour plot indicating the auxiliary voltage relative tothe phase (x-axis) of auxiliary RF generator 14 and the rail voltageV_(RAIL) (y-axis) output by agile DC power supply of FIG. 2. Theauxiliary voltage is generally described as the voltage at auxiliaryelectrode 40 and may be measured using peak-to-peak or Root Mean Square(RMS) techniques. The contour lines of FIG. 10B indicate the auxiliaryvoltage at auxiliary electrode 40. Of particular interest, by waynon-limiting example, is point 424 of FIG. 10B. For a given phase x=nand rail voltage V_(RAIL) y=n, the auxiliary voltage Level=V_(R5), asshown at point 424.

FIGS. 11A and 11B are contour plots depicting a transition from aninitial condition represented by FIGS. 10A and 10B to a second conditionrepresented by FIGS. 11A and 11B. For example, in various embodiments,FIGS. 10A and 10B can represent the delta phase versus the phase andrail voltage V_(RAIL) (for FIG. 10A) and the auxiliary voltage versusthe phase and rail voltage V_(RAIL) (FIG. 10B) for a RF power deliverysystem in which auxiliary match network 28 is configured so that atunable element of auxiliary match network 28 is in a first position.FIGS. 11A and 11B represent the corresponding delta phase versus phaseand rail voltage V_(RAIL) (FIG. 11A) and auxiliary voltage versus phaseand rail voltage V_(RAIL) (FIG. 11B) when the tunable element ofauxiliary match network 28 is displaced to a second position. In variousembodiments, the tunable element can be adjusted from a first positionto a second position.

With reference to FIGS. 10A and 11A, selected point 422 represents phasea=rail voltage V_(RAIL)=b, and the resulting delta phase Level=0. Asshown in FIG. 10A, point 422 is located on contour line delta phase=0.Following the transition, the position of the contour lines change,where contour values −D₂, −D₁, . . . , D₄ represent the same values inFIGS. 10A and 11A. In various embodiments, it is preferred that point422 remain on the same counter line, such as delta phase=0, in thisnon-limiting example. In order to remain on the same contour line, point422 must transition from point 422 in FIG. 10A to point 422′ in FIG.11A. This transition occurs along arrow 426. In order to move from point422 to point 422′, it is necessary to adjust both the phase from x=a tox=a′ and the rail voltage V_(RAIL) from y=b to y=b′ in order to maintainthe position of point 422 on contour line delta phase=0.

Likewise, in FIG. 10B, point 424 is shown for phase x=m, rail voltageV_(RAIL)=n, and auxiliary voltage Level=V_(R5). The contour lines forV_(R1), . . . , V_(R7) in FIGS. 10B and 11B represent similar values.Point 424 in FIG. 10B is shown along contour line V_(R5). In order tomaintain point 424 on contour line V_(R5), point 424 of FIG. 10Btransitions to point 424′ along arrow 428 of FIG. 11B. As FIG. 11Bdemonstrates, it is necessary to vary both the phase to x=m′ and therail voltage V_(RAIL) to y=n′ in order to maintain point 424 alongcontour line V_(R5), such as shown at point 424′. Thus, in each instanceof translation of point 422 to point 422′ as shown in FIGS. 10A and 11Aand point 424 to point 424′ as shown in FIGS. 10B and 11B, it isnecessary to reduce the phase setpoint and increase the rail voltageV_(RAIL). Thus, FIGS. 10A and 10B and FIGS. 11A and 11B demonstrate, invarious embodiments, that it is necessary to control both phase and railvoltage V_(RAIL) in order to maintain the position along a predeterminedcontour line.

FIGS. 12A and 12B depict contour plots of delta phase versus phase andrail voltage V_(RAIL) in FIG. 12A and auxiliary voltage versus phase andrail voltage V_(RAIL) in FIG. 12B. Each contour plot in FIGS. 12A and12B depicts a point 428 corresponding to a phase=d, a rail voltageV_(RAIL)=e, and a delta phase=f in FIG. 12A and an auxiliary voltage=gin FIG. 12B. Plots 430 and 432 and respective contour plots of FIGS. 12Aand 12B indicate a challenge to approaching a rail voltage V_(RAIL) andphase solution in each of FIGS. 12A and 12B.

As shown in FIG. 12A, in the area around point 428, changing the railvoltage V_(RAIL) significantly affects the delta phase, since point 428is in a position where the contour lines are generally parallel to therail voltages V_(RAIL). The change in delta phase correspondinglyaffects convergence to point 428 in FIG. 12B. Further, as shown in FIG.12B, the auxiliary voltage contours V₁, . . . , V₁₂ are parallel to thephase values so that small phase actuator changes significantly affectthe voltage. Similarly, in FIG. 12B, the auxiliary voltage contour linesV₁, . . . , V₁₂ are generally perpendicular to the rail voltage V_(RAIL)values. Therefore, large rail voltage V_(RAIL) changes are needed tomake small changes in the auxiliary voltage. Accordingly, waveforms 430and 432 indicate a circling around the desired endpoint 428 by changingthe phase and the rail voltage V_(RAIL) using independent control loopsin order to arrive at a desired setpoint on a selected contour.

FIGS. 12A and 12B demonstrate a particular challenge to variousconfigurations of the RF power supply system 10 of FIG. 1 in whichadjusting a single input presents challenges to accurate control of theauxiliary voltage. It can be seen that significant increases in one ofthe phase or rail voltage V_(RAIL) are necessary in order to change theposition of a point, such as point 428, along a contour line and minorchanges in the other variable result in significant changes in theposition of point 428 along a contour line. Thus, a single input systemcan result in certain challenges in which a single input is varied inorder to adjust a particular output.

By way of comparison, FIG. 13 indicates a contour plot in which the railvoltage V_(RAIL) can be varied in order to adjust the position of apoint, such as point 440. In FIG. 13, point 440 corresponds to a phaseof x=h, rail voltage V_(RAIL) y=i, and a resulting auxiliary voltage=j.FIG. 13 presents a condition in which varying one of the inputs, whetherthe phase along the x-axis or the rail voltage V_(RAIL) along the y-axisenables adjustment of point 440 along a contour line, such as alongcontour line V_(T5) with reasonable resolution. In contrast, FIGS. 12Aand 12B do not enable such resolution by adjusting one of the phasealong the x-axis or V_(RAIL) along the y-axis.

FIG. 14 depicts a linear-quadratic-integral (LQI) control system for, invarious embodiments, controlling the agile DC power supply actuator(rail voltage V_(RAIL)) and phase actuator (phase) of auxiliary RFgenerator 14 of FIGS. 1-4. The LQI configuration of FIG. 14 providesoptimal control in which controller gains are determined based onminimization of a cost function. Such a configuration utilizes bothinternal measurements and output feedback for controlling selectedparameters of auxiliary RF generator 14. The control system of FIG. 14is inherently multi-input, multi-output (MIMO). In various embodiments,performance is highly tunable, including enabling individual adjustmentfor feedback errors, states, and actuator amplitudes.

In FIG. 14, control system 480 receives an input value r, whichrepresents a vector or a matrix, which is the auxiliary voltage setpointand setpoint for the delta phase or phase difference between the mainand auxiliary RF signals:

$\begin{matrix}{r = \begin{bmatrix}r_{Aux} \\r_{{Delta}\mspace{14mu} {Phase}}\end{bmatrix}} & (1)\end{matrix}$

where:

r_(Aux) represents the setpoint for the voltage of the RF waveformapplied to the auxiliary electrode; and

r_(Delta Phase) represents the setpoint for the phase difference ordelta phase between the master and auxiliary RF waveforms.

The setpoint r is compared to system output:

$\begin{matrix}{y = {\begin{bmatrix}y_{1} \\y_{2}\end{bmatrix} = \begin{bmatrix}V_{Aux} \\\Delta_{Phase}\end{bmatrix}}} & (2)\end{matrix}$

where:

y₁=V_(Aux) represents the measured voltage of the RF waveform applied tothe auxiliary electrode; and

y₂=Δ_(Phase) represents the measured phase difference between main RFwaveform and the auxiliary RF waveform.

The input r is applied to a summer 482 which determines a difference orerror, represented as a matrix or vector e. The matrix or vector erepresents the difference between the auxiliary voltage setpoint r_(Aux)and the measured auxiliary voltage output y_(Aux) and the differencebetween the delta phase setpoint r_(Delta Phase) and the measured deltaphase output Δ_(Phase). That is:

$\begin{matrix}{e = {\begin{bmatrix}e_{Aux} \\e_{{Delta}\mspace{14mu} {Phase}}\end{bmatrix} = {{r - y} = {{\begin{bmatrix}r_{Aux} \\r_{{Delta}\mspace{14mu} {Phase}}\end{bmatrix} - \begin{bmatrix}V_{Aux} \\\Delta_{Phase}\end{bmatrix}} = \begin{bmatrix}{r_{Aux} - V_{Aux}} \\{r_{{Delta}\mspace{14mu} {Phase}} - \Delta_{Phase}}\end{bmatrix}}}}} & (3)\end{matrix}$

where:

e_(Aux) represents the error or difference between the commanded RFvoltage applied to the load and the actual RF voltage applied to theload; and

e_(Delta Phase) represents the error or difference between the commandedand actual phase difference between the main signal and the auxiliary RFsignal.

The error e is input to an integrator 484 and the integrated errorvalues, represented by a matrix or vector x_(j), is applied to block488. The matrix or vector x_(j), can be represented as follows:

$\begin{matrix}{x_{j} = \begin{bmatrix}x_{3} \\x_{4}\end{bmatrix}} & (4)\end{matrix}$

where:

x₃ represents the integral of the auxiliary electrode error output byintegrator 486; and

x₄ represents the integral of the phase difference error output byintegrator 486.

Block 488 receives the integrated error values e and also receives amatrix or vector of values x which includes the internal states outputby system block 490. The matrix or vector x is represented as follows:

$\begin{matrix}{x = {\begin{bmatrix}x_{1} \\x_{2}\end{bmatrix} = \begin{bmatrix}x_{Rail} \\x_{Phase}\end{bmatrix}}} & (5)\end{matrix}$

where:

x₁=x_(Rail) represents the measured auxiliary rail voltage state outputby system 490, as will described further below; and

x₂=x_(Phase) represents the measured auxiliary phase state output bysystem 490. Block 488 is a gain block which applies a feedback gainmatrix K to generate a control matrix or vector u to system block 490.The matrix or vector u is represented as follows:

$\begin{matrix}{u = \begin{bmatrix}u_{1} \\u_{1}\end{bmatrix}} & (6)\end{matrix}$

where:

u₁ represents the commanded rail voltage V_(Rail) for the auxiliary RFgenerator; and

u₂ represents the commanded phase of the RF waveform output by theauxiliary RF generator.

System block 490 is responsive to input u to adjust the auxiliaryvoltage output y_(aux) and the phase output y_(phase).

The LQI or state representation depicted in FIG. 14 replaces an n^(th)order differential equation with a single first order matrixdifferential equation. In the control system 480 of FIG. 14, u describedabove in equation (6) can be further described as shown below:

$\begin{matrix}{u = {\begin{bmatrix}u_{1} \\u_{2}\end{bmatrix} = {\begin{bmatrix}{K_{11}K_{12}K_{13}K_{14}} \\{K_{21}K_{22}K_{23}K_{24}}\end{bmatrix}\begin{bmatrix}x_{1} \\x_{2} \\x_{3} \\x_{4}\end{bmatrix}}}} & (7)\end{matrix}$

where:

K₁₁, K₁₂, K₂₁, and K₂₂ represent the state feedback;

K₁₃ and K₁₄ represent correction constants for the auxiliary voltage;

K₂₃ and K₂₄ represent correction constants for the phase actuator; and

x₁, x₂, x₃, and x₄ are as described above.

In various embodiments, K₁₁, K₁₂, K₂₁, and K₂₂, are configured with therecognition that because the auxiliary voltage and phase voltage reactquickly, only minimal secondary effects exist. Accordingly, K₁₁, K₁₂,K₂₁, and K₂₂ are used to approximate slewing dynamics of the auxiliaryvoltage and phase. In various embodiments, the K constants are set inaccordance with predetermined contours used to characterize theauxiliary RF generator at the time of manufacture. The slope between thecontours is used to determine the K values. In various embodiments, theK constants are set based on in-situ measurements of the contours forthe auxiliary RF generator for a given operating condition.

FIG. 15A depicts a plot of the auxiliary voltage relative to the phaseon the x-axis and the rail voltage V_(RAIL) on the y-axis. While invarious representations, auxiliary voltage can be represented by shadingor color, or FIGS. 15A and 15B include multiple quadrants, includingquadrants 500, 502 . . . , 510. Similarly, FIG. 15B depicts a plot ofphase offset versus phase on the x-axis and rail voltage V_(RAIL) on they-axis. The various quadrants 512, 514, . . . , 522 indicate the phaseoffset between the master RF generator 12 and auxiliary RF generator 14.

FIGS. 16A and 16B correspond to respective FIGS. 15A and 15B, with FIGS.16A and 16B indicating the respective auxiliary voltage and phase offsetin response to when the contour lines are arranged such that the RFpower system may oscillate when converging to a solution, such as inFIGS. 12A and 12B. Accordingly, quadrants 500′, 502′, . . . , 510′ inFIG. 16A indicate the location of the quadrants 500, . . . , 510 of FIG.15A under such convergence-challenged conditions. As can be seen in FIG.16A, the shape of the auxiliary voltage from FIG. 15A has been reflectedabout an approximately 45 degree angle line. Similarly, the plot of FIG.15B has been displaced such that the position of the contours have beensimilarly reflected around an approximately 45 degree angle line. Thepositions of respective points 512′, 514′, . . . , 518′ indicate thereflection of the corresponding quadrants of FIG. 15B.

FIGS. 17A-17D depict plots of various respective electrical parametersrelative to time using proportional-integral control according tovarious embodiments under conditions in which contour lines are arrangedin a configuration to facilitate convergence to a predeterminedauxiliary voltage and delta phase solution. Accordingly, FIG. 17Aindicates a waveform 540 of a rail voltage setpoint. FIG. 17B indicatesa waveform 542 of the auxiliary voltage. FIG. 17C indicates a waveform544 of a phase setpoint. FIG. 17D indicates a waveform 546 of a deltaphase between a master RF generator 12 and an auxiliary RF generator 14.As can be seen at time T₁, when the RF generator moves into closed-loopoperation after power-up, the auxiliary voltage correspondinglyincreases and the delta phase decreases. Both the auxiliary voltage 542and the delta phase 546 reach stability almost instantaneously.

FIGS. 18A-18D depict waveforms corresponding to the electricalcharacteristics of respective FIGS. 17A-17D. In FIGS. 18A-18D, theauxiliary voltage contour lines and/or the delta phase contour lines arearranged such that convergence to a predetermined solution results inseeking or hunting about a desired solution endpoint. Waveform 540′corresponds to a rail voltage V_(RAIL), waveform 542′ corresponds toauxiliary voltage, waveform 544′ corresponds to phase setpoint, andwaveform 546′ corresponds to delta phase. At time T₁, the RF generatoroutput is powered up in open-loop mode to a pre-defined starting pointfor both the rail voltage and phase actuators. At time T₂, the RFgenerator enters closed-loop operation. Rail voltage 540′ and auxiliaryvoltage 542′ are seen to exhibit an instability at T₂, and, to a lesserdegree, phase setpoint 544′ and delta phase 546′ also exhibit aninstability. At T₃ the RF generator output is disabled prior to shuttingdown. As can be seen in FIGS. 18A-18D, under selected conditions therail voltage and phase actuators system tends to oscillate.

FIGS. 19 and 20 depict waveforms for FIGS. 19A-19D and FIGS. 20A-20Ddepicting the similar electrical characteristics to waveforms forrespective FIGS. 17A-17D and/or FIGS. 18A-18D. FIGS. 19A-19D and FIGS.20A-20D, however, indicate system response using control described withrespect to FIG. 14. Waveform 560 depicts the rail voltage V_(RAIL) forauxiliary RF generator 14, waveform 562 depicts the auxiliary voltageapplied to auxiliary electrode 40 of coupling network 24, waveform 564depicts the phase setpoint for auxiliary RF generator 14, and waveform566 depicts the delta phase between the RF signals applied to respectivemaster electrode 32 and auxiliary electrode 40. Waveforms 560′, 562′,564′, and 566′ depict waveforms for similar electrical characteristics.

FIGS. 19A-19D depict waveforms in which the contour plots for a RFsystem are arranged to facilitate convergence to a predetermined point.The waveforms of FIGS. 19A-19D represent an embodiment in which controlis provided using the control model of FIG. 14. FIGS. 20A-20D, on theother hand, depict control implemented by the control support system ofFIG. 14 for a configuration where the delta phase and the auxiliaryvoltage contour lines are arranged so that the rail voltage V_(RAIL)and/or phase setpoint may hunt for a solution. As shown in FIGS. 19A-19Dand FIGS. 20A-20D, utilizing the control provided in FIG. 14 indicatesthat waveforms 560′, 562′, 564′, 566′ converge to stability relativelyquickly with respect to the waveforms of nominal conditions 560, 562,564, 566. As can be seen in FIGS. 19A-19D and 20A-20D, at T₁, thecontroller enters a learning phase. The actuators are steered through apre-defined sequence and the auxiliary voltage and delta phase outputsare recorded. Using the information, the contour slopes for the currentoperating condition are calculated. These are then used to update the Kmatrix of controller gains. At time T₂, the RF generator enters aclosed-loop mode of operation with these updated gain parameters. Thesystems of FIGS. 19A-19D and 20A-20D converge to stability relativelyquickly with minimal oscillation. Thus, it can be seen that the systemof FIG. 14 provides convergence regardless of the configuration of thecontour lines for delta phase and/or auxiliary voltage.

FIG. 21 shows a control module 569. The control module or controller 110of FIGS. 2-4 may be implemented as control module 569. Control module569 may include auxiliary RF voltage module 568, phase difference module570, voltage compare module 572, phase compare module 574, DC voltagemodule 576, and phase output module 578. In various embodiments, controlmodule 569 includes a processor that executes code associated with themodules 568, 570, 572, 574, 576, and 578. Operation of the modules 568,570, 572, 574, 576, and 578 is described below with respect to themethod of FIG. 22.

For further defined structure of the control module of FIGS. 2-4, seebelow provided method of FIG. 22 and the below provided definition forthe term “module”. The systems disclosed herein may be operated usingnumerous methods, an example RF control system method of which isillustrated in FIG. 22. Although the following operations are primarilydescribed with respect to the implementations of FIGS. 2-4, theoperations may be easily modified to apply to other implementations ofthe present disclosure. The operations may be iteratively performed.Although the following operations are shown and primarily described asbeing performed sequentially, one or more of the following operationsmay be performed while one or more of the other operations are beingperformed.

FIG. 22 depicts a flowchart 580 of a multi-input, multi-output controlsystem for controlling, by way of non-limiting example, auxiliary RFgenerator 14 of RF power system 10 of FIG. 1. The method begins at startblock 582 and proceeds to blocks 584 and 586. At block 584, auxiliary RFvoltage module 568 of control module 569 measures the voltage output ofauxiliary RF generator 14, such as via auxiliary voltage sensor 66. Atblock 586, phase difference module 570 of control module 569 measuresthe phase difference between the respective RF output signals of masterRF generator 12 and auxiliary RF generator 14. It should be noted thatblocks 584 and 586, in various embodiments, can be executed in parallel,as shown in FIG. 22 or, in various other embodiments, can be executedsequentially.

Once the output voltage of auxiliary RF generator 14 and the phasedifference between auxiliary RF generator 14 and master RF generator 12are determined, control proceeds to decision block 588. At decisionblock 588, two separate decision inputs are considered. At block 590,voltage compare module 572 of control module 569 determines if themeasured output voltage is within range of or equal to a predeterminedsetpoint. At block 592, phase compare module 574 of control module 569determines if the phase difference is within range of or equal to apredetermined value (Delta). As shown at block 588, if the voltage isequal to a predetermined setpoint and the phase difference is equal to apredetermined difference Delta, control proceeds back to blocks 584 and586. In other words, no adjustment of the output voltage or phasedifference is necessary. Further at block 588, if either the voltage isnot equal to a predetermined setpoint or the phase difference is notequal to a predetermined difference Delta, control proceeds to block594.

Block 594 implements multi-input, multi-output control of both thevoltage setpoint of the auxiliary voltage and the phase differencebetween master RF generator 12 and auxiliary RF generator 14. Thus, twoinputs may be adjusted or controlled in response to one or both of theauxiliary voltage not being at a predetermined setpoint or the phasedifference not being at a predetermined value Delta. At block 596, DCvoltage module 576 of control module 569 generates a control signal toadjust the output of the agile DC power supply, such as shown at item170 of FIG. 2, in order to vary the output voltage of auxiliary RFgenerator 14. At block 598, phase output module 578 of control module569 determines the phase setpoint of auxiliary RF generator in order toadjust the phase difference to a predetermined value Delta. At block598, phase output module 578 causes auxiliary RF generator 14 togenerate a request to master RF generator 12 in order to effect acorresponding adjustment to the phase auxiliary RF generator 14.

Block 594 is configured to demonstrate the interaction between adjustingthe output of agile DC power supply to vary the rail voltage V_(RAIL)and adjusting the phase of auxiliary RF generator 14. Link 600 indicatescommunication between the respective blocks 596, 598. That is, DCvoltage module 576 and phase output module 578 communicate. Accordingly,block 594 indicates an implementation of a control such as describedwith respect to the control system of FIG. 14. Thus, flowchart 580demonstrates a multi-input, multi-output control of the rail voltageV_(RAIL) via adjusting DC power supply 170 of FIG. 2 and the phasecontrol, such as provided via RF control signal 54.

The foregoing description is merely illustrative in nature and is in noway intended to limit the disclosure, its application, or uses. Thebroad teachings of the disclosure can be implemented in a variety offorms. Therefore, while this disclosure includes particular examples,the true scope of the disclosure should not be so limited since othermodifications will become apparent upon a study of the drawings, thespecification, and the following claims. It should be understood thatone or more steps within a method may be executed in different order (orconcurrently) without altering the principles of the present disclosure.Further, although each of the embodiments is described above as havingcertain features, any one or more of those features described withrespect to any embodiment of the disclosure can be implemented in and/orcombined with features of any of the other embodiments, even if thatcombination is not explicitly described. In other words, the describedembodiments are not mutually exclusive, and permutations of one or moreembodiments with one another remain within the scope of this disclosure.

Spatial and functional relationships between elements (for example,between modules, circuit elements, semiconductor layers, etc.) aredescribed using various terms, including “connected,” “engaged,”“coupled,” “adjacent,” “next to,” “on top of,” “above,” “below,” and“disposed.” Unless explicitly described as being “direct,” when arelationship between first and second elements is described in the abovedisclosure, that relationship can be a direct relationship where noother intervening elements are present between the first and secondelements, but can also be an indirect relationship where one or moreintervening elements are present (either spatially or functionally)between the first and second elements. As used herein, the phrase atleast one of A, B, and C should be construed to mean a logical (A OR BOR C), using a non-exclusive logical OR, and should not be construed tomean “at least one of A, at least one of B, and at least one of C.”

In the figures, the direction of an arrow, as indicated by thearrowhead, generally demonstrates the flow of information (such as dataor instructions) that is of interest to the illustration. For example,when element A and element B exchange a variety of information butinformation transmitted from element A to element B is relevant to theillustration, the arrow may point from element A to element B. Thisunidirectional arrow does not imply that no other information istransmitted from element B to element A. Further, for information sentfrom element A to element B, element B may send requests for, or receiptacknowledgements of, the information to element A.

In this application, including the definitions below, the term “module”or the term “controller” may be replaced with the term “circuit.” Theterm “module” may refer to, be part of, or include: an ApplicationSpecific Integrated Circuit (ASIC); a digital, analog, or mixedanalog/digital discrete circuit; a digital, analog, or mixedanalog/digital integrated circuit; a combinational logic circuit; afield programmable gate array (FPGA); a processor circuit (shared,dedicated, or group) that executes code; a memory circuit (shared,dedicated, or group) that stores code executed by the processor circuit;other suitable hardware components that provide the describedfunctionality; or a combination of some or all of the above, such as ina system-on-chip.

The module may include one or more interface circuits. In some examples,the interface circuits may include wired or wireless interfaces that areconnected to a local area network (LAN), the Internet, a wide areanetwork (WAN), or combinations thereof. The functionality of any givenmodule of the present disclosure may be distributed among multiplemodules that are connected via interface circuits. For example, multiplemodules may allow load balancing. In a further example, a server (alsoknown as remote, or cloud) module may accomplish some functionality onbehalf of a client module.

The term code, as used above, may include software, firmware, and/ormicrocode, and may refer to programs, routines, functions, classes, datastructures, and/or objects. The term shared processor circuitencompasses a single processor circuit that executes some or all codefrom multiple modules. The term group processor circuit encompasses aprocessor circuit that, in combination with additional processorcircuits, executes some or all code from one or more modules. Referencesto multiple processor circuits encompass multiple processor circuits ondiscrete dies, multiple processor circuits on a single die, multiplecores of a single processor circuit, multiple threads of a singleprocessor circuit, or a combination of the above. The term shared memorycircuit encompasses a single memory circuit that stores some or all codefrom multiple modules. The term group memory circuit encompasses amemory circuit that, in combination with additional memories, storessome or all code from one or more modules.

The term memory circuit is a subset of the term computer-readablemedium. The term computer-readable medium, as used herein, does notencompass transitory electrical or electromagnetic signals propagatingthrough a medium (such as on a carrier wave); the term computer-readablemedium may therefore be considered tangible and non-transitory.Non-limiting examples of a non-transitory, tangible computer-readablemedium are nonvolatile memory circuits (such as a flash memory circuit,an erasable programmable read-only memory circuit, or a mask read-onlymemory circuit), volatile memory circuits (such as a static randomaccess memory circuit or a dynamic random access memory circuit),magnetic storage media (such as an analog or digital magnetic tape or ahard disk drive), and optical storage media (such as a CD, a DVD, or aBlu-ray Disc).

The apparatuses and methods described in this application may bepartially or fully implemented by a special purpose computer created byconfiguring a general purpose computer to execute one or more particularfunctions embodied in computer programs. The functional blocks,flowchart components, and other elements described above serve assoftware specifications, which can be translated into the computerprograms by the routine work of a skilled technician or programmer.

The computer programs include processor-executable instructions that arestored on at least one non-transitory, tangible computer-readablemedium. The computer programs may also include or rely on stored data.The computer programs may encompass a basic input/output system (BIOS)that interacts with hardware of the special purpose computer, devicedrivers that interact with particular devices of the special purposecomputer, one or more operating systems, user applications, backgroundservices, background applications, etc.

The computer programs may include: (i) descriptive text to be parsed,such as HTML (hypertext markup language), XML (extensible markuplanguage), or JSON (JavaScript Object Notation) (ii) assembly code,(iii) object code generated from source code by a compiler, (iv) sourcecode for execution by an interpreter, (v) source code for compilationand execution by a just-in-time compiler, etc. As examples only, sourcecode may be written using syntax from languages including C, C++, C#,Objective-C, Swift, Haskell, Go, SQL, R, Lisp, Java®, Fortran, Perl,Pascal, Curl, OCaml, Javascript®, HTML5 (Hypertext Markup Language 5threvision), Ada, ASP (Active Server Pages), PHP (PHP: HypertextPreprocessor), Scala, Eiffel, Smalltalk, Erlang, Ruby, Flash®, VisualBasic®, Lua, MATLAB, SIMULINK, and Python®.

None of the elements recited in the claims are intended to be ameans-plus-function element within the meaning of 35 U.S.C. § 112(f)unless an element is expressly recited using the phrase “means for,” orin the case of a method claim using the phrases “operation for” or “stepfor.”

What is claimed is:
 1. A RF system comprising: a first RF generatorconnected to a first electrode of a load and generating a first RFsignal to the first electrode; a second RF generator connected to asecond electrode of a load and generating a second RF signal to thesecond electrode, wherein the first and second RF generators provide arespective RF voltage to the first and second electrodes; and acontroller for controlling the second RF generator, the controllergenerating a control signal to at least one of the first RF generator orthe second RF generator, wherein the first RF generator and the secondRF generator operate at substantially a same frequency in accordancewith a RF control signal communicated from the first RF generator to thesecond RF generator, wherein the second RF generator communicates arequest to the first RF generator via the second digital communicationport to request adjustment of pulsing of the second RF signal, and thefirst RF generator varies a pulse control signal applied to the secondRF generator to adjust pulsing of the second RF signal.